In 1962 a major step forward was taken with the Reliant Regal 3/25 which replaced the Reliant Regal Mk VI. This new 3-wheeler had a unitary construction body of re-enforced fibreglass. Fibreglass was moulded in two major units (outer and inner) and then bonded together and bolted to a steel chassis. This made this the first Reliant to have a fibreglass floor rather than the wooden floor from the previous side-valve Regals. The body came in both a Saloon version and a Van version that followed in 1963. The windscreen was now full size and winding side windows were back (complemented by opening quarter light windows) and remained a feature on all future 3-wheelers. Another new addition was the introduction of a heater that used hot water from the system to provide warm air for de-misting the windscreen and for warming up the interior.

Power came from Reliants new all aluminium 600cc water cooled four-cylinder OHV engine which helped give the Regal 3/35 a fuel economy of around 65 mpg and 25 hp (hence the name 3/25 - 3 wheels / 25hp). This engine also had a water pump, up until now the side-valve units used a thermo-cycle system. The Regal 3/25 is easily distinguished by the large slats at the front of the vehicle. It was essentially a Regal Mk VII though given how radically different it was compared with the Mk VI, it is surprising that Reliant kept the Regal name rather than rename it as a totally new vehicle.

In 1965 the Regal 3/25 Super was launched and sold as "a more luxurious" version of the standard 3/25. Reliant dropped the price of the standard 3/25 and contiuned to sell it along the Super 3/25 until stocks were depleted. The Regal 3/25 Super received a new streamlined frontal (replacing the slats), smoother rear styling, refined trim, a new dashboard, repositioned hand brake and enlarged door pockets. In addition it also came in a new range of six colours. Reliant's production of the Regal was so popular that it in 1969 the fifty thousandth Regal was delivered.

Minor changes were made again in 1969 and the engine had now increased to 700cc giving 30 hp hence the new name for the vehicle; the Reliant Regal 3/30. With the one hundred thousandth Regal being manufactured in 1972 production went on to produce just over 110,000 Regals before manufacture ceased in 1973 making it the worlds best selling 3-wheeler. No other Reliant model exceeded this.

In 1967 a Regal 21E Saloon and Van was also introduced. The 21E was so called as it had 21 extras fitted at the factory. The extra 21 items were:

It is often questioned whether the Reliant Regal existed in a "GT" and a "Safari" model. It did though the models were not made by Reliant. A Reliant dealer called "Two Strokes Ltd" in Middlesex would take a standard Regal and modify them with the necessary changes to make either the GT or Safari model. The GT was based around a Reliant Regal 3/30 saloon whilst the Safari was based upon a Reliant Regal Supervan III. The extras that made the Safari stand out from standard Supervans included:

1 Black roof

2 Polished wheel trims

3 Non-rust grille trims

4 Steering wheel glove

5 T.S. easy oil filter

6 Black Custom flashes

7 “Safari” mudflaps

8 Amber roof window

9 Dash-reading oil level indicator

10 Folding rear seat

11 “Thruflow” air ventilation

12 Passenger seat

Along side the saloons Regal 5cwt vans were also made that range from the Supervan, the Supervan II and the Supervan III. The differences being as updates that were applied to the saloons. Reliant never referred to the vans as a Regal, simply just Reliant Supervan. As the Robin was also to have the "Super" prefix, Supervans are now often referred to as Reliant Regal Supervan to define it as being a Regal and not a Robin Supervan. Production of the Regal ceased in 1973 with the introduction of the Reliant Robin.